This invention relates generally to communications systems, and more particularly to single sideband digital communications systems.
This invention has as a background, U.S. Pat. Nos. 4,742,532 and 5,185,765 covering VPSK, the entire disclosures of which are hereby incorporated by reference herein. U.S. Pat. No. 5,930,303, which covers VMSK and VMSK/2, is also background, the entire disclosure of which is also hereby incorporated by reference herein.
U.S. Pat. No. 5,930,303 discusses aperture encoding the entire disclosure of which is also hereby incorporated by reference herein as if being set forth in its entireties. Finally, a paper xe2x80x9cSpectrally Efficient Biphase Modulationxe2x80x9d by Dr. C. Koukourlis, Dr. J. Sahalos, Mr. John Pliatsikas and the Mr. Harold Walker, the inventor hereof, deals with a similar method involving a different encoding algorithm. This paper appeared in the May 1998 Issue of Applied Microwaves and Wireless magazine. An expanded version of this paper with more mathematical detail is published in xe2x80x9cThird Generation Mobile Systemsxe2x80x9d, edited by Dr. P. Stavroulakis, published by Springer Verlag, Berlin, in the fall of 1999.
The present invention relates to a new and novel single sideband digital communications system that does not require an RF carrier for reception, reduces the bandwidth required to far less than that required by most methods and has an excellent to superior Bit Energy to Noise ratio for a given bit error rate. The method is self clocking, can tolerate rapid changes in frequency, such as Doppler effects for example, and tends to cancel or ignore interference of various kinds so that the Signal-to-Noise Ratio (SNR) can approach Shannon""s Limit for usable error rates.
It is the object of the present invention to encode the data into a single frequency while improving the SNR required for a given Bit Error Rate (BER) while simultaneously reducing undesired emissions so as to more easily meet applicable regulatory requirements.
A method of modulating a phase reversing pulse train including a plurality of signal pulses each having an associated period of a given temporal duration to encode a multiplicity of input data bits each having a data state, and prevent losses of clock timing, the method comprising the steps of identifying select ones of the input data bits which repeat the data state of a respectively preceding one of the input data bits; identifying select ones of the pulses which correspond to the select bits; and, alternately shortening and lengthening the periods associated with the select ones of the pulses.